it is usually much easier to define initial conditions explicitly, as documented below (rather
than by using the IC command).See the Command Reference for a discussion of the TIMINT and IC commands.
Zero initial displacement and nonzero initial velocity - The nonzero velocity is established by applying
small displacements over a small time interval on the part of the structure where velocity is to be spe-
cified. For example if
ɺo
= 0.25, you can apply a displacement of 0.001 over a time interval of 0.004,
as shown below.
...
TIMINT,OFF! Time integration effects off
D,ALL,UY,.001! Small UY displ. (assuming Y-direction velocity)
TIME,.004! Initial velocity = 0.001/0.004 = 0.25
LSWRITE! Write load data to load step file (Jobname.S01)
DDEL,ALL,UY! Remove imposed displacements
TIMINT,ON! Time integration effects on
...Nonzero initial displacement and nonzero initial velocity - This is similar to the above case, except that
the imposed displacements are actual values instead of "small" values. For example, if uo = 1.0 and
ɺ = 2.5, you would apply a displacement of 1.0 over a time interval of 0.4:
...
TIMINT,OFF! Time integration effects off
D,ALL,UY,1.0! Initial displacement = 1.0
TIME,.4! Initial velocity = 1.0/0.4 = 2.5
LSWRITE! Write load data to load step file (Jobname.S01)
DDELE,ALL,UY! Remove imposed displacements
TIMINT,ON! Time integration effects on
...Nonzero initial displacement and zero initial velocity - This requires the use of two substeps (NSUBST,2)
with a step change in imposed displacements (KBC,1). Without the step change (or with just one substep),
the imposed displacements would vary directly with time, leading to a nonzero initial velocity. The ex-
ample below shows how to apply uo = 1.0 and
ɺ
= 0.0:...
TIMINT,OFF! Time integration effects off for static solution
D,ALL,UY,1.0! Initial displacement = 1.0
TIME,.001! Small time interval
NSUBST,2! Two substeps
KBC,1! Stepped loads
LSWRITE! Write load data to load step file (Jobname.S01)
! Transient solution
TIMINT,ON! Time-integration effects on for transient solution
TIME,...! Realistic time interval
DDELE,ALL,UY! Remove displacement constraints
KBC,0! Ramped loads (if appropriate)
! Continue with normal transient solution procedures
...Nonzero initial acceleration - This can be approximated by specifying the required acceleration (ACEL)
over a small interval of time. For example, the commands to apply an initial acceleration of 9.81 would
look like this:
...
ACEL,,9.81! Initial Y-direction acceleration
TIME,.001! Small time interval
NSUBST,2! Two substeps
KBC,1! Stepped loadsRelease 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationTransient Dynamic Analysis